Lead Actresses playing different characters

[rebooted]

We know that Shannen Doherty was initially supposed to play Piper 

and the HMC was supposed to play Prue

But recently I was thinking how I could have seen Shannen play Piper (I think she would have done well) and HMC playing Phoebe with another actress playing Prue

Or I could have seen Shannen play Prue and Piper play Phoebe. 

I could only see Alyssa Milano playing Phoebe and maybe Paige. 

Does anyone else see a different configuration or thought another actress could play another character. 

Could Daryl have also been Leo?

[Aaeiyn]

Shannen Doherty as Phoebe Halliwell.
Holly Marie Combs as Prue Halliwell.
Alyssa Milano as Paige Matthews.
Rose McGowan as Piper Halliwell.